1. Field of the Invention
The present invention relates to reclosable plastic bags of the type in which perishable food products and other goods are packaged for sale to consumers in retail outlets. More specifically, the present invention relates to reclosable plastic bags manufactured and concurrently filled on horizontal or vertical form-fill-and-seal (FFS) machines, wherein a plastic interlocking zipper for each bag is disposed transversely relative to the direction of motion of the thermoplastic sheet material used to form the reclosable bags on the FFS machine.
2. Description of the Prior Art
The present invention relates to improvements in the package-making art and may be practiced in the manufacture of thermoplastic bags and packages of the kind that may be used for various consumer products, but which are particularly useful for food products which must be kept in moisture- and air-tight packages, free from leakage until initially opened for access to the product contents, which packages are then reclosable by zipper means to protect any remainder of the product therein.
The indicated art is fairly well-developed, but nevertheless remains susceptible to improvement contributing to increased efficiency and cost effectiveness.
One problem that still hampers the production of packages from continuous zipper-equipped sheet material is the difficulty in attaining a satisfactory sealing of the bag or package against leakage, where the zipper and area of film engaged by the zipper extends through the side (cross) seal areas separating one bag or package from the next. This problem occurs where the zipper is longitudinal with respect to the direction of motion of the thermoplastic sheet material used to form the reclosable bags on the FFS machine, in which case the transverse, or side, sealing bars must flatten and seal the zipper at the same time as they are sealing the thermoplastic sheet material from which the packages are being made. The difficulty with which this is consistently and successfully achieved is reflected by the high occurrence of leaking packages.
Numerous attempts have been made to solve this problem. Among the approaches that have been taken is the substitution of a transverse zipper for the longitudinal zipper. Where such a zipper is provided the transverse sealing bars associated with the FFS machine do not flatten the zipper as they are making a side seal, although they may seal the zipper to the thermoplastic sheet material transversely thereacross without flattening it.
The present invention relates to the provision of a transverse zipper for reclosable plastic bags or packages being manufactured on either a horizontal or vertical FFS machine. More specifically, the present invention is both a zipper strip and a method for securing the zipper strip transversely across the thermoplastic sheet material from which reclosable bags are being produced on a FFS machine.